Distributed terminal optical transmission system

ABSTRACT

The invention facilitates optical signals generated from customer premise equipment (CPE) at the edges of the metro domain networks. The CPEs are connected to extension terminals that transform the optical signal originating at the CPE into a suitable format for long haul transmission. The optical signal then propagates to a primary terminal where the signal is multiplexed with other optical signals from other extension terminals. The multiplexed signals are then transmitted over LH or ULH network to a second primary terminal where the signal is then demultiplexed from other optical signals and transmited to the proper extension terminal. At the extension terminal, the demultiplexed optical signal is transformed from its LH format back into a format suitable for inter-connection to a CPE. Using this architecture, the signal under goes optical-to-electrical conversion only at the extension terminals or end points. These end points can be located in lessee&#39;s facility. The only equipment located in lessor&#39;s facility is the primary terminal containing line amplifiers and add/drop nodes.

CROSS-REFERENCE TO RELAYED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/402,840 filed Mar. 27, 2003, which claims benefit of U.S. ProvisionalApplication No. 60/368,545, filed Mar. 29, 2002, each of which is herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to a computer system for transporting opticalsignals between coupled metro domains using an optical transportnetworking system and more particularly using a lessor's opticaltransport networking system to transport a lessee's signal.

BACKGROUND OF THE INVENTION

The transmission, routing and dissemination of information has occurredover computer networks for many years via standard electroniccommunication lines. These communication lines are effective, but placelimits on the amount of information being transmitted and the speed ofthe transmission. With the advent of light-wave technology, a largeamount of information is capable of being transmitted, routed anddisseminated across great distances at a high rate over fiber opticcommunication lines.

In traditional optical networks, long haul (LH) and ultra-long haul(ULH) optical networks typically connect major cities. The LH and ULHoptical networks can span local geographical regions, countries,continents and even large bodies of water. The construction andmaintenance costs of these long haul and ultra-long haul opticalnetworks are prohibitively large. Because of these prohibitive costs,few communication service providers own their own optical networks. Manycommunication service providers lease the right to transmit opticalsignals over another communication service provider's optical network.The communication service providers that construct their nationalnetworks through the leasing of the optical networks from othercommunication service providers incur disadvantages, including increasedcost versus chose communication service providers that own their ownoptical networks.

A typical communication service provider leasing “space” on anothercommunication service provider's optical network must provide opticaldata networking equipment at their own local facilities in ametropolitan area and must also provide optical data networkingequipment at the lessor's facility which may be in the same metropolitanarea or a short distance away in another metropolitan area. In additionto the cost of maintaining multiple sets of optical data networkingequipment, there is an additional penalty from the requirement to usemetro transmission systems to connect the lessee communication systemprovider's facility to the lessor communication service provider'sfacility and then to use the LH and ULH optical data networkingequipment to traverse the LH and ULH optical network. This systemresults in excessive optical-to-electrical conversions and increases theoperational complexity of the overall systems.

What is needed is an optical transmission system that would locate allterminal equipment in the lessee's facility. It would also be beneficialif only line amplifiers and add/drop nodes were in the lessor'sfacilities. The signal should undergo optical-to-electrical conversiononly at the endpoints, preferably in the lessee's facility and at anyregeneration points required by physical constraints.

SUMMARY OF THE INVENTION

The present invention provides an architecture and method fortransmitting signals over a network which allows for all of lessee'sequipment to be located at a extension terminal in lessee's facility. Itallows for efficient optical-to-electrical conversions and does notrequire multiple sets of optical data networking equipment.

Prior art systems suffer from the limitation that a typicalcommunication service provider leasing “space” must provide optical datanetworking equipment at their own local facilities and must also provideoptical data networking equipment at the lessor's facility. In additionto the cost of maintaining multiple sets of optical data networkingequipment, there is an additional penalty from the requirement to usemetro transmission systems to connect the lessee communication systemprovider's facility to the lessor communication service provider'sfacility and then to use the LH and ULH optical data networkingequipment to traverse the LH and ULH optical network. This systemresults in excessive optical-to-electrical conversions and increases theoperational complexity of the overall systems. In addition, prior artsystems suffer from the requirement to convert customer premiseequipment signals into short haul format for transport to a facility,usually a lessor's, and then at the facility, to be converted into a LHformat for transport over a LH network. Certain prior art systems haveattempted to address these problems with varying success.

U.S. Pat. No. 5,726,784 to Alexander, et al., entitled WDM OPTICALCOMMUNICATION SYSTEM WITH REMODULATORS AND DIVERSE OPTICAL TRANSMITTERS,discloses an invention which is capable of placing information fromincoming information-bearing optical signals onto multiple opticalsignal channels for conveyance over an optical waveguide. A receivingsystem is configured to receive an information bearing optical signal ata particular reception wavelength and each receiving system must includeat least one Bragg grating member for selecting the particular receptionwavelength. However, Alexander is intended to provide compatibility withexisting systems and does not disclose or suggest a system that allowsfor efficient optical-to-electrical conversions or one that would locateall terminal equipment in the lessee's facility.

U.S. Pat. No. 5,613,210 to Van Driel, et al., entitled TELECOMMUNICATIONNETWORK FOR TRANSMITTING INFORMATION TO A PLURALITY OF STATIONS OVER ASINGLE CHANNEL, discloses an invention which uses a method wherein asignal to be transmitted is modulated on a subcarrier having its ownfrequency and then modulated on a main carrier in each sub-station.While Van Driel does utilize subcarrier multiplexing, only twowavelengths are involved and the multiplexing is therefore limited. VanDriel does not disclose transmitting the signals over a LH network. Nordoes Van Driel disclose or suggest a system that allows for efficientoptical-to-electrical conversions or one that would locate all terminalequipment in the lessee's facility.

U.S. Pat. No. 5,559,625 to Smith, et al., entitled DISTRIBUTIVECOMMUNICATIONS NETWORK, discloses a method and system for increasing theamount of re-use of information transmission wavelengths within anetwork. A distributive communications network includes groups of nodesat different levels. At each level of nodes, wavelength traffic iseither passed on to a higher level, or looped back according to the bandof wavelengths to which it is assigned. Philip does not disclose orsuggest a system that allows for efficient optical-to-electricalconversions or one that would locate all terminal equipment in thelessee's facility.

Other patents such as U.S. Pat. No. 5,778,116 to Tomich, entitledPHOTONIC HOME AREA NETWORK FIBER/POWER INSERTION APPARATUS, and U.S.Pat. No. 5,914,799 to Tan, entitled OPTICAL NETWORK disclose aninvention that is limited to signal transfer from a central station tosubscriber stations. Neither of the patents disclose a method orapparatus for transmitting signals over a LH network, disclose orsuggest a system that allows for efficient optical-to-electricalconversions or one that would locate all terminal equipment in thelessee's facility.

The present invention is an improvement over the prior art because itallows for efficient optical-to-electrical conversions and does notrequire multiple sets of optical data networking equipment. The presentinvention provides for coupled metro domain networks which are a part ofa larger inter-domain network. The invention facilitates optical signalsgenerated from customer premise equipment (CPE) at the edges of themetro domain networks. The CPEs are connected to extension terminalspreferably in lessee's facility. The extension terminals transform theoptical signal originating at the CPE into a suitable format for longhaul transmission. One or more CPEs may be connected to one or moreextension terminals. The optical signal then propagates from anextension terminal to a primary terminal along a metro fiber. At theprimary terminal, the optical signal is multiplexed with other opticalsignals from other extension terminals. The multiplexed signals are thentransmitted over LH or ULH network to a second primary terminal via corefiber. The optical signal may propagate along the core fiber with thehelp of a chain of amplifiers and optical add/drops. The second primaryterminal then demuxes the optical signal from other optical signals andtransmits the demuxed signal to the proper extension terminal. At theextension terminal, the demuxed optical signal is transformed from itsLH format back into a format suitable for inter-connection to a CPE.Using this architecture, the signal under goes optical-to-electricalconversion only at the extension terminals. These extension terminalscan be located in lessee's facility. The only equipment located inlessor's facility is the primary terminal containing line amplifiers andadd/drop nodes. The transport system meets the networking requirementsof intercity connections without the need for complex and costly metrotransport gear. Also, the core extension terminals may be physicallydistributed across several metro network nodes.

The invention will be better understood from the following more detaileddescription taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS

A better understanding of the invention can be obtained from thefollowing detailed description of one exemplary embodiment as consideredin conjunction with the following drawings in which:

FIG. 1 is a block diagram depicting a prior art inter-domain opticalnetworking between core networks and metro/regional networks;

FIG. 2 is a block diagram of the detail of the prior art end-terminalsand the interconnections between optical transport systems in FIG. 1;

FIG. 3 is a block diagram depicting an inter-domain optical transportsystem according to the present invention;

FIG. 4 is a block diagram of the detail of a primary terminal for use inthe present invention;

FIG. 5 is a block diagram of a type one extension terminal for use inthe present invention;

FIG. 6 is a block diagram of a type two extension terminal for use inthe present invention;

FIG. 7 is a block diagram showing a multiplexer-demultiplexerarchitecture based on optical interleaver and deinterleaver filters foruse in the present invention;

FIG. 8 is a block diagram showing a multiplexer-demultiplexerarchitecture based on banded DWDM filters for use in the presentinvention;

FIG. 9 is a block diagram showing a tunable demultiplexer architecturefor use in the present invention;

FIG. 10 is a block diagram showing a tunable multiplexer for use in thepresent invention;

FIG. 11 is a block diagram of shelf configurations according to thepresent invention; and

FIGS. 12 a and 12 b are block diagrams of alternate shelf configurationsaccording to the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the descriptions that follow, like parts are marked throughout thespecification and drawings with the same numerals, respectively. Thedrawing figures are not necessarily drawn to scale and certain figuresmay be shown in exaggerated or generalized form in the interest ofclarity and conciseness. Reference of an A-Z signal or direction meansfrom the left side of the drawing to the right side of the drawing whileZ-A means from the right side to the left side. The A-Z or Z-Adesignation is used for illustrative purposes only.

The prior art as it relates to optical transport networking betweendomains is shown in FIG. 1 and FIG. 2. Referring to FIG. 1, an opticaltransport network may be composed of several domains: a core network 100with a geographic extent of typically between 100 km and 1500 km and aplurality of metro network domains 130 a-d with geographic extentstypically of 3 km to 100 km.

Customer premise equipment (CPE) 190 a-h are considered to be outsidemetro domains 130 a, 130 b, 130 c, and 130 d. CPE 190 a-h is sometimesreferred to as client equipment or end-user equipment. CPE 190 a-h areconnected to metro domain 130 a-d via interoffice fiber, 151 c, 151 d,151 e, 151 j-l, and 151 p-s.

Metro domains 130 a-d vary widely in extent interconnection, and in thetypes of systems that are deployed within them. Metro domain 130 a showsa plurality of ring-protected systems. Metro domain 130 a is composed ofprimary ring end terminal 135 a, extension ring end terminal 136 a,primary multi-node terminal 145, and extension multi-node terminals 146a and 146 b. Optical signals are propagated to and from primary ring endterminal 135 a and extension ring end terminal 136 a on metro fibers 152a and 152 b. Optical signals may propagate on either or both legs of thering so that in the event fiber 152 a or fiber 152 b fails, a connectionis continually maintained between primary ring end terminal 135 a andextension ring end terminal 136 a.

A more complex, multi-node protected ring is indicated by primarymulti-node ring end terminal 145 and extension multi-node ring endterminals 146 a and 146 b, whereby, all three nodes are interconnectedvia metro fiber 152 c and 152 d. Metro fiber 152 c and 152 d may be asingle fiber or a plurality of fibers. Methods for ring protection arewell known in the art and will not be discussed further.

Metro domain 130 b is different from metro domain 130 a in that metrodomain 130 b consist of primary end terminals 125 a-c and extension endterminals 126 a-c being connected by metro fiber 152 e-g in a linearfashion as opposed to a ring protected system as shown in metro domain130 a. Metro domain 130 b provides a network consisting of a pluralityof unprotected linear links where the optical signals are propagatedalong a single path of fiber in an unprotected way. For example, ifmetro fiber 152 e is cut or fails, then optical signals terminating atand originating from CPE 190 d will no longer be connected with core endterminal 110 c. By the interconnection of CPE 190 e to extension endterminals 126 b and 126 c and extension end terminals 126 b and 126 cbeing connected to core end-terminal 110 c via primary end terminal 125b and 125 c an economical path protection can be realized at the clientequipment layer. Path protection at the client equipment layer isrealized because if one interconnection of CPE 190 e to either extensionend terminal 126 b or 126 c fails, the other interconnection can stilltransmit signals to 110 c.

Metro domain 130 c indicates a combination of protected and unprotectedlinks. Primary end terminal 125 d is connected to extension end terminal126 d in a linear fashion via fiber 152 h. Primary end terminal 135 b isconnected to extension end terminal 136 b in a ring-protected system viafibers 152 i and 152 j. Primary end terminal 125 e is connected toextension end terminal 126 e via metro fiber 152 k. Core end terminal110 b is ultimately connected to CPE 190 h by the transiting link ofprimary end terminal 125 f and extension end terminal 126 f in domain130 d via fiber 152 m and by the transiting link of primary end terminal125 e and extension end terminal 126 e in domain 130 c via fiber 152 k.Secondary end terminal 126 e is connected to primary end terminal 125 fvia multiple fiber 151 r. Such architecture may occur, for example,because the geographical distance between core end terminal 110 b andCPE 190 h is too large for one domain. More relevant to this invention,the situation may occur because different entities own and manage thetwo domains 130 c and 130 d and there is no way to connect domain 130 dto core end-terminal 110 b without some type of intermediate equipmentand associated fiber.

Metro-systems may multiplex more than one optical signal onto a singlefiber using methods that are well known in the art as such as code wavedivision multiplexing (CWDM), wavelength division multiplexing (WDM), ordense wavelength division multiplexing (DWDM) methods. Starting fromcore end-terminal 110 b in the core network 100, a plurality oftributary signals are interconnected and terminated on primary endterminal 125 e via multiple fiber 151 o. Primary end terminal 125 emuxes the plurality of tributary signals together and transmits themuxed signals to extension end terminal 126 e via metro fiber 152 k.Secondary end terminal 126 e demuxes the plural tributary signals andtransmits them via multiple pairs of intra-office fibers 151 r toprimary end terminal 125 f in domain 130 d. Primary end terminal 125 fmuxes the plurality of tributary signals together and transmits themuxed signals to extension end terminal 126 h via metro fiber 152 m.Finally, extension end terminal 126 h demuxes the plural tributarysignals and connects them, via multiple intra-office fibers 151 s to CPE190 h where the signals terminate. If the signals originated at CPE 190h the process would be reversed.

Core network 100 is sometimes referred to as a long haul network and maybe composed of a plurality of linear DWDM systems or more complex ringstructures employing SONET ADMs or a mix of each type. A linear DWDMsystem is shown in FIG. 1. Signals are transferred into and out of corenetwork 100 by core end terminals 110 a-c via intra-office fiber 151 a,151 b, 151 f-i, and 151 m-o. The tributary interfaces will be describedin more detail in FIG. 2 as are the methods used to transmit signalsthrough the core end terminals 110 a-c. The transmitted signals from onecore end terminal 110 a-c propagate through a set of core opticalamplifiers 115 a-d and optical add-drop multiplexing device (OADM) 116on core fiber 150 a, 150 x, and 150 z before reaching a second core endterminal 110 a, 110 b, and 110 c where the signals are transmitted intoa metro network domain 130 a-d.

Core amplifiers 115 a-d perform the function of compensating for loss ofoptical signal power as the optical signals propagate through core fiber150 a, 150 x, and 150 z. The amplifiers are spaced typically 60 km to120 km apart. The ellipsis in the drawing indicates that there could beany number amplifiers between 115 a and 115 b and between 115 c and 115d. Also, there may be more than one OADM along core fiber 150 a, 150 xand 150 z. OADM 116 performs the function of extracting and insertingoptical signals from core fiber 150 a, 150 x and 150 z, and placing oracquiring the signals on or from intra-office fiber 151 a, 151 b, 151f-i, and 151 m-o.

In FIG. 2, the details of signals paths from core fiber 150 (shown as ablock), core end terminal 110, primary end terminals 125 g and 125 h, tothe metro fiber 152 n and 152 o (shown as blocks) are shown. Thesesignals paths occur between, for example, 110 c and 125 a-c in FIG. 1.With the exception of core fiber 150 and metro fiber 152 n and 152 o,all the elements of FIG. 2 are physically co-located in a metro centraloffice (CO) or a core network point-of-presence (POP) facility.Moreover, typically all end-terminal components in core end terminal 110and metro terminal 125 g and 125 k must be co-located in the samefacility and within adjacent bays according to prior art.

Continuing in FIG. 2, intra-office fibers usually consist of a fiberpair, for example intra-office fiber 151 t-1 and 151 u-1, whereby thetransmit and receive optical signals usually propagate on separatefibers. Optical or WDM signals from core fiber 150 enter core endterminal 110 via intra-office fiber 151 t-1. Intra-office fiber 151 t-1is connected to optical amplifier 155 where the propagating signals areamplified. Optical amplifier 155 is further connected to DWDM demux 165via core end terminal fiber 161 a. Core end terminal fiber 161 a carriescomposite optically muxed signals. The composite signals aredeconstructed into their constituent and individual optically modulatedsignals by DWDM demux 165 and appear on fiber interconnects 163 a-c.Optical signals on fiber interconnects 163 a-c are received by Long Haul(LH) transponders 160 a-c. LH transponders 160 a-c electrically processand optically remodulate the signals, and transmit the LH remodulatedsignals through tributary interfaces 151 v-1 and 152 v-2 to short haul(SH) transponders 170 a and 170 b or SH transceiver 180 via intra-officefibers 151 v-3.

LH transponders 160 a-c may be varied in their capability andcomposition. For example, they may employ internal modulation orexternal modulation using NRZ, RZ, or other formats as known by thoseskilled in the art. LH transponders 160 a-c have the primary function ofconverting short and intermediate reach intra-office signals typicallygenerated by directly modulated lasers to long reach signals; long reachsignals (LH format) being compatible with intercity propagation ofhundreds or thousands of kilometers.

The SH transponders 170 a and 170 b and SH transceiver 180 may be ofdifferent varieties typically found in metro domain systems and knownwell to those skilled in the art. The distinguishing feature of SHtransponder 170 a and 170 b and SH transceiver 180 from LH transponders160 a-c is in the propagation distance limitation on the SH transponders170 a and 170 b and SH transceiver 180. SH transponders 170 a and 170 band SH transceiver 180 have a propagation distance limited to less thanor about 80 km.

The term transponder applies to both the LH and SH applications whereinthe input optical signal to the device is narrow band and occurs at aparticular input wavelength or frequency and wherein the device convertsthe input signal to an output optical signal of a different wavelengthor frequency and may be narrowband or broadband in nature. In general, atransponder will operate in full-duplex mode. The term transceiverapplies to a device that converts input signals at a particularwavelength or frequency to an output signal at the same wavelength orfrequency while maintaining similarity between the optical bandwidth anddispersive capacity of the input signal to the optical bandwidth anddispersive capacity of the output signal.

Both LH and SH devices perform the functions of regeneration oramplification and reshaping, and may or may not employ retiming. Furtherdetails of the LH or SH receiver technology and transmitter technology,that is the transponders and transceivers, are known in the art and willnot be described further.

Continuing the description of FIG. 2, the optical signals onintra-office fibers 151 v-1, 151 v-2, and 151 v-3 are received by SHtransponders 170 a and 170 b and SH transceiver 180. The optical signalson 151 v-3 are converted by transponder 180 to optical signals thatpropagate directly on the intra-office fibers 151 x-2 to metro fiber 152o. Alternatively, the optical signals appearing on intra-office fiber151 v-1 and 151 v-2 are converted by SH transponders 170 a and 170 b,respectively, to intermediate signals and transmitted to WDM mux 175 viafiber interconnect 173 a and 173 d, respectively. WDM mux 175 muxes theintermediate signals and transmits them to the metro fiber 152 n viaintra-office fiber 151 x-1 and ultimately to a extension end terminal.

In the Z-A direction, optical signals from metro fiber 152 n propagatealong intra-office fiber 151 y-1 to WDM demux 176. WDM demux 176extracts the optical signals propagated along intra-office fiber 151y-1, and transmitts the extracted signals to SH transponders 170 a and170 b via interconnects 173 b and 173 c. SH transponders 170 a and 170 belectronically process and optically remodulate the extracted signalsfor transport over a SH network and transmit the remodulated signals toLH transponders 160 a and 160 b via intra-office fibers 151 w-1 and 151w-2. LH transponders 160 a and 160 b convert the signals for into aformat suitable for LH transporting and transmits the prepared signalsto DWDM mux 166 via fiber interconnects 163 d and 163 e.

Optical signals from metro fiber 152 o propagate along intra-officefiber 151 y-2 to SH transceiver 180. SH transceiver 180 electronicallyprocesses and optically remodulates the extracted signals for transportover a SH network and transmits the remodulated signal to LH transponder160 c via intra-office fiber 151 w-3 and tributary interface 155 c. LHtransponder converts the signal into a format suitable for LHtransporting and transmits the prepared signal to DWDM mux 166 via fiberinterconnect 163 f.

DWDM mux 166 muxes the signals received from fiber interconnects 163 d-fand transmits the muxed signals to transmitting optical amplifier 156via core end terminal fiber 161 b. Transmitting optical amplifier 156amplifies the muxed signals and transmits the amplified signals to corefiber 150 via intra-office fiber 151 u-1.

The preferred and alternate embodiments of the invention are describedwith reference to FIGS. 3-12. Beginning with FIG. 3, the inventionincludes a set of coupled metro networks 230 a-d which are a part of alarger inter-domain network 200. The metro networks 230 a-d areconnected by a plurality of linear DWDM systems or more complex ringstructures employing SONET ADMs or a mix of each type. A linear DWDMsystem is shown in FIG. 3, but the invention encompasses otherstructures. The invention facilitates optical signals generated from CPE290 a-p at the edges of metro networks 230 a-d to be interconnecteddirectly with each other. CPEs 290 a-p are the same type as CPEs 190 a-hshown in FIG. 1. Those skilled in the art will recognize that theconfiguration of metro network domains may take many forms and thatthose depicted are exemplary. Similarly, the invention can be applied toa widely varying arrangement of interconnections of metro opticnetworks, as will be appreciated by those skilled in the art. CPEs 290a-d, 290 f-i and 290 l-p are in communication with extension terminals220 a-h via intra-office fiber 251 a-d, 251 g-i and 251 o-s.Intra-office fibers 251 a-s are the same type of fiber as intra-officefibers 151 a-s shown in FIG. 1. CPE 290 d is connected to primaryterminal 210 a via intra-office fiber 251 e. CPE 290 e is connected toprimary terminal 210 c via intra-office fiber 251 f. CPEs 290 j and 290k are connected to primary terminal 210 b via intra-office fibers 251 kand 251 l.

Extension terminals 220 a-f are connected to primary terminals 210 a and210 c via metro fiber 252 b-d and 252 f-h. Metro fiber 252 a-k is thesame type of fiber as metro fiber 152 a-m. Primary terminals 210 a and210 c are connected to junctions 211 a and 211 b via metro fiber 252 aand 252 e. Extension terminal 220 g is connected to junction 211 c viametro fiber 252 i. Extension terminal 220 h is connected to junction 211e via metro fiber 252 k. Junction 211 e is connected to junction 211 dvia metro fiber 252 j. Junction 211 a is connected to core amplifier 215a via core fiber 250 a. Amplifiers 215 a-d are the same type ofamplifiers as 115 a-d. Core fiber 250 a, 250 x and 250 z is the sametype of fiber as core fiber 150 a, 150 x and 150 z.

Junction 211 b is connected to OADM 216 via interoffice fiber 251 u.Junctions 211 c and 211 d are connected to primary terminal 210 b viaintra-office fiber 251 m and 251 n. Also connected to primary terminal210 b are CPE 290 j and 290 k through intra-office fiber 251 k and 251l.

To accomplish the interconnection of metro networks 230 a, 230 b, 230 c,230 d, core optical amplifiers 215 a-d are connected to OADM 216 viacore fiber 250 a, 250 x and 250 z. The ellipses in the drawing indicatethere can be any number of core amplifiers 215 a-d between junction 211a and OADM 216 and between primary distributed terminal 210 b and OADM216. Also, there may be more than one OADM 216 along core fiber 250 a,250 x and 250 z. Either OADM 216 or core amplifiers 215 a-d areconnected to a sub-system of primary terminals 210 a-c and extensionterminals 220 a-h composed of terminal shelves. CPE 290 a-p may beinterconnected directly to primary terminals 210 a-c or extensionterminals 220 a-h to accomplish the transfer of optical signals from aparticular CPE to a different CPE that may be in a geographicallydistinct location. OADM 216 can be fixed or not fixed as in broadcastand select architectures. In the preferred embodiment, OADM 216 includesa broadcast and select architecture as is known in the art. Core opticalamplifiers 215 and OADM 216 may or may not contain components to performoptical dispersion compensation and other components to perform gainequalization, both of which may employ techniques known in the art.

Referring to FIG. 3, a link between CPE 290 a and CPE 290 p in the A-Zdirection of a full-duplex signal path will now be described as anexample. CPE 290 a is connected to extension terminal 220 a viaintra-office fiber 251 a. Extension terminal 220 a transforms the signaloriginating at 290 a into a suitable format for LH transmission.Extension terminal 220 a transmits the transformed signal to primaryterminal 210 a via metro fiber 252 b. At primary terminal 210 a, thetransformed signal is optically muxed with other signals from extensionterminals 220 b and 220 c and with signals generated at CPE 290 d. Themultiplexed signals are transmitted to junction 211 a via metro fiber252 a. At junction 211 a, metro fiber 252 a is connected to core fiber250 a and the optical signal propagates along core fiber 250 a, 250 xand 250 z through the chain of core amplifiers 215 a-d and OADM 216 tothe primary distributed terminal 210 b. At primary distributed terminal210 b, the desired signal for CPE 290 p is optically demuxed from theother signals and transmitted along intra-office fiber 251 n to junction211 d. At junction 211 d, intraoffice fiber 251 n is coupled to metrofiber 252 j. The desired optical signal propagates along metro fiber 252j to junction 211 e. At junction 211 e, metro fiber 252 j is coupled tometro fiber 252 k. The desired optical signal continues to propagate onmetro fiber 252 k to extension terminal 220 h. At extension terminal 220h, the desired optical signal is received and transformed from its LHformat into a format suitable for interconnection with CPE 290 p throughintra-office fiber 251 s. The optical signal terminates at CPE 290 p. Inthe Z-A direction of the full duplex signal can be described in asimilar way, so that signals originating from CPE 290 p and terminatingat CPE 290 a are propagated in a similar manner.

There are many optical links that can be established in the inter-domainnetwork 200. For example, the present invention allows for CPE 290 c tobe interconnected to any one of the other CPE shown in FIG. 3. Also,more than one CPE may be connected to a single extension terminal orprimary terminal. For example, CPE 290 a and CPE 290 b are bothconnected to extension terminal 220 a CPE 290 a and 290 b may beco-located together or geographically separate and neither CPE 290 a or290 b need be co-located with extension terminal 220 a. Although inpractice they are usually co-located and interconnected by intra-officefiber 251 a and 251 b as shown. Additionally, one CPE may be connectedto a plurality of extension terminals or primary terminals. For example,CPE 290 c is shown having at least two distinct optical interfaces, onebeing connected to extension terminal 220 b and the other connected toextension terminal 220 c. By interconnecting extension terminals 220 band 220 c to primary terminal 210 a with metro fiber 252 c and 252 d, aprotected connection can be made between CPE 290 c and primary terminal210 a. If a fiber failure occurs on either metro fiber 252 c or 252 dthe other metro fiber 252 c or 252 d may carry the optical signalssafely from CPE 290 c to other points in inter-domain network 200.

Another link example will illustrate further features of the currentinvention. Simultaneous multiple interconnections between metro networks230 b and 230 c consisting of links between CPE 290 e to CPE 290 o, CPE290 h to CPE 290 k, and CPE 290 i to CPE 290 p is described. Inparticular, CPEs 290 h and 290 i are connected to extension terminal 220f via intra-office fiber 251 i and 251 j, respectively. Secondaryterminal 220 f converts the originating signals from CPEs 290 h and 290i to a LH format. Secondary terminal 220 f optically muxes the convertedsignals and transmits the muxed signals to primary terminal 210 c viametro fiber 252 h. Also, CPE 290 e is connected to primary terminal 210c via intra-office fiber 251 f and transmits an SH signal to primaryterminal 210 c.

At primary terminal 210 c, the optical signal originating from CPE 290 eis converted to a LH format and optically muxed with the other opticalsignals originating from extension terminal 220 f. The muxed opticalsignals from primary terminal 210 c propagate on metro fiber 252 e tojunction 211 b. The signals propagate through junction 211 b tointra-office fiber 251 u and continues on to OADM 216. OADM 216 muxesthe signals from intra-office fiber 251 u onto core fiber 250 x. Theoptical signals propagate on core fiber 250 x and 250 z towards primaryterminal 210 b. Multiple core amplifiers 215 c and 215 d may be used toboost the signal. Additional OADMs 216 may also be present on core fiber250 x and 250 z.

At primary terminal 210 b, the optical signals on core fiber 250 z areoptically demuxed in such a way that optical signals destined for CPE290 e and CPE 290 i are transmitted on intra-office fiber 251 n whileoptical signals destined for CPE 290 h are transmitted on intra-officefiber 251 l. The signal on intra-office fiber 251 l terminates at CPE290 k and the signal from CPE 290 h has been successfully transmitted toCPE 290 k. CPE 290 k is considered local to core distributed terminal210 b.

The signals originating from CPE 290 e and CPE 290 i on intra-officefiber 251 n propagate along intra-office fiber 251 n through junction211 d and onto metro fiber 252 j inside metro network 230 c. The LHsignals propagate along metro fiber 252 j through junction 211 e andonto metro fiber 252 k inside metro network 230 d. The optical signalspropagate along metro fiber 252 k to extension terminal 220 h. Atextension terminal 220 h, the optical signals are demuxed and convertedfrom a LH format to a format suitable for interconnection to CPEs 290 oand 290 p. The converted signals are transmitted to CPEs 290 o and 290 pvia intra-office fiber 251 r and 251 s, respectively, where the signalsterminate. The signal from CPE 290 e has been successfully transmittedto CPE 290 and the signal from 290 i has been successfully transmittedto 290 p. In the Z-A direction of the full duplex signal can bedescribed in a similar way so that originating signals from 290 k, 290r, and 290 q destined for 290 h, 290 e, and 290 i respectively, arepropagated in a similar manner to that just described.

The above explains how a signal may propagate through more than onemetro network 230 without conversion from an LH format. In the preferredembodiment, the links between primary terminals 210 a-c and extensionterminals 220 a-h may be more than 100 km and may include opticalamplifiers with or without dispersion compensators and gain equalizers.

The invention allows for primary terminals 210 a-c to be placed outsideor within a metro network 230 as required by the location of CPEs 290a-p. Primary terminals 210 a and 210 c are inside respective metronetworks 230 a and 230 b while primary terminal 210 b is outside metronetworks 230 c and 230 d.

The invention also allows for remote interconnections between OADM 216and primary terminals 210 a-c to be of distances greater than thosefound in most interoffice networks. The distance for the remoteinterconnection is similar in nature to the long distances betweenprimary terminals 210 a-c and extension terminals 220 a-p and could bearound 100 km. Interconnection between primary terminals 210 a-c,extension terminals 220 a-h and OADM 216 are accomplished with a singlepair of fibers. This feature is further described in relation to FIG. 4.

FIG. 4 depicts the preferred embodiment of a primary terminal. Primaryterminal 210 allows for the interconnection of full duplex signals fromcore fiber 250 (shown as a block) to various distinct CPEs 290 s-x. CPEs290 s-x are the same type as CPEs 290 a-p FIG. 3 and CPEs 190 a-hFIG. 1. CPEs 290 s-x maybe geographically diverse from one another. Inthe A-Z direction, an LH format optical signal is transmitted from thecore fiber plant 250 to receiving amplifier 255 via intra-office fiber251 v-1. Intra-office fibers 251 v-a, 251 x-1,251 x-2, 251 x-3, 251 y-1,251 y-2, 251 y-3, 251 z-1, 251 z-2, 251 z-3, 251 z-4, 251 z-5, 251 z-6,251 w-1 are the same type of fiber as intra-office fibers 251 a-s and151 a-s. Receiving amplifier 255 performs the function of amplifying theincoming multiplexed WDM or DWDM signals from intra-office fiber 251 v-1to a known level, so the signal has enough optical power to transmit toother components such as extension terminals 220 i-k. The amplifiedsignal is transmitted to fine demux 265 via fiber 261 a. The signal cancontain any number of muxed optical signals. In the preferredembodiment, there are twelve optical signals, referred to as M (12) todenote any arbitrary number of twelve signals.

Fine demux 265 demuxes the M (12) muxed signals in such a way as toleave N (4) smaller groups of M/N (3) optical signals. The N (4) smallergroups are muxed onto 4 intra-office fiber interconnections 271 a-d.These smaller groups of approximately M/N (3) optical signals will becalled “optical mux groups” or simply “mux groups” hereinafter. One muxgroup on intra-office fiber interconnection 271 a remains inside theprimary terminal 210 for further processing while the other mux groupson intra-office fiber interconnections 271 b-d exit for distribution todistinct locations, such as CPE 290 v-x.

The mux group on fiber interconnection 271 a is transmitted from finedemux 265 to coarse demux 267. Coarse demux 267 demuxes theapproximately M/N (3) optical signals into individual optical signalsand transmits the individual signals to transponders 260 a-c via outputfiber connections 263 a-c. Transponders 260 a-c convert the individualLH format signals into optical signals for transmission on intra-officeoptical fibers 251 x-1, 251 x-2, and 251 x-3. The transmitted opticalsignals are suitable for use by CPEs 290 s-u, and therefore the primaryterminal 210 serves as the interface device for the local traffic(optical signals) intended for CPEs 290 s-u. As shown by the ellipsis,there may be a plurality of CPEs 290 connected to any one of thetransponders 260 a-c.

For the delivery of remote traffic (optical signals) to remote CPE 290v-x, fine demux 265 transmits the mux groups on intra-office fiberinterconnections 271 b-d to metro fiber 252. The optical mux groups aretransported from metro fiber 252 to extension terminals 220 i-k viageographically distinct fiber interconnections 271 e-i. Secondaryterminals 220 i-k demux the optical mux groups into individual opticalsignals and transmit the individual signals to CPEs 290 v-x viaintra-office fibers 251 z-1, z-3, and z-5. As shown by the ellipsis,there may be a plurality of CPEs connected to any one of the extensionterminals 220 i-k.

The optical signals, being in full duplex, also flow in a directionopposite to that just described and in a similar way. Individual opticalsignals that originate from CPE 290 v-x are transmitted to extensionterminals 220 i-k via intra-office optical fibers 251 z-2, z-4, z-6.Secondary terminals 220 i-j mux the optical signals into optical muxgroups and transmit the mux groups to metro fiber 252 via fiberinterconnections 271 f, 271 h, and 271 j. The optical mux groupspropagating on metro fiber 252 are transmitted to fine mux 266 via fiberinterconnections 271 f-h. The optical mux groups are muxed into one muxgroup by fine mux 266. Fine mux 266 transmits a signal containing themux group to output amplifier 256 via fiber 261 b. Output amplifier 256then amplifies the signal for transmission on intra-office fiber 251 w-1to core fiber 250.

Similarly, optical signals originating from CPEs 290 s-u flow in the Z-Adirection through transponders 260 a-c via intra-office fiber 151 y-1,151 y-2 and 151 y-3. Transponders 260 a-c convert the individual opticalsignals to a LH format and send the converted signals to coarse mux 268via output fiber connection 263 d-f. Coarse mux 268 muxes the convertedsignals together into an optical mux group and transmitts the opticalmux group to fine mux 266 via fiber interconnection 271 e. The opticalmux groups propagating on fiber interconnections 271 e-h are muxed intoone mux group by fine mux 266. Fine mux 266 transmitts the signalcontaining the mux group to output amplifier 256 via fiber 261 b. Outputamplifier 256 then amplifies the signal for transmission on intra-officefibers 251 w-1 to core fiber 250. The combination of primary terminal210 and extension terminals. 220 i-k form a system of distributedterminals, which is a preferred embodiment of the present invention.

In FIG. 5, the preferred embodiment of a type one extension terminal 220is shown. A mux group containing approximately M/N, for example 3,optical signals is propagated from metro fiber 252 (shown as a block) toterminal 220 via fiber interconnection 271 k. The mux group traversesterminal 220 receiving amplifier 285 which may be or may not be the sametype of amplifier as receiving amplifier 255 in primary terminal 210,FIG. 4. Terminal 220 receiving amplifier 285 amplifies the incomingapproximately M/N (3) multiplexed optical WDM or DWDM signals from 271 kto a known level so the signals have enough optical power to betransmitted to the other components in type one extension terminal 220and connecting devices such as CPE 290 aa-cc. The approximately M/N (3)multiplexed optical signals are transmitted from extension terminalreceiving amplifier 285 to extension terminal coarse demux 287 viaextension terminal interconnection 281 a. Secondary terminal coarsedemux 287 demuxes the approximately M/N (3) multiplexed optical signalsinto individual optical signals for transmission to transponders 260 d-fvia extension terminal output fiber connections 283 a-c. Transponders260 d-f are the same type of transponders as transponders 260 a-c inFIG. 4.

Transponders 260 d-f convert the LH format optical signals on extensionterminal output fiber connections 283 a-c into signals suitable for useby CPEs 290 aa-cc. Transponders 260 d-f are connected to CPE 290 aa-ccvia intra-office fibers 251 aa-1, 251 aa-2 and 251 aa-3.

Terminal 220 serves as the interface device for the local traffic(optical signals) intended for CPE 290 aa-cc. Intra-office fibers 251aa-1, 251 aa-2 and 251 aa-3 are usually physically co-located withterminal 220, but they may incorporate long reach capability includingoptical amplifiers to connect to an individual port on a remote CPE 290via an intra-office fiber.

The full duplex optical signals also flow in the Z-A direction, fromCPEs 290 aa-cc through intra-office fibers 251 bb-1, 251 bb-2 and 251bb-3 to transponders 260 d-f. Transponders 260 d-f convert the signalformats used by CPEs 290 aa-cc to a LH format. The converted LH formatsignals are sent to extension coarse mux 288 via extension terminaloutput fiber connections 283 d-f. Secondary terminal coarse mux 288combines the optical signals into an optical mux group and transmits theoptical mux group to optical amplifier 286 via extension terminalinterconnection 281 b. The mux group is amplified by terminal 220transmitting optical amplifier 286 for propagation along fiberinterconnection 271 m to metro fiber 252 and on to a primary terminal210 (FIG. 4).

The preferred embodiment of a type one extension terminal 220 is capableof transmitting and receiving signals from primary terminal 210 fromdistances on the order of but possibly even larger than 100 km Fordistances much larger than 100 km a stand-alone optical amplifier orchain of such devices can be inserted between the extension terminalsand the primary terminal.

A type two extension terminal 225 is depicted in FIG. 6. Terminal 225,can be used for short distance connections, of the order of 5 km orless, that require a physical separation between the primary terminal210 and multiple CPEs. The primary difference between a type twoextension terminal 225 and type one extension terminal 220 is thatreceiving optical amplifier 285 and transmitting amplifier 286 are notfound in type two terminal 225. With the exception of the opticalamplifiers, the signal propagation is the same to that described fortype one extension terminal 220.

In the A-Z direction, an optical mux group containing approximately M/Noptical signals are propagated from metro fiber 252 (shown as a block)to type two extension terminal 225 via fiber interconnection 271 p. Theoptical mux group propagates to short extension coarse demux 297. Coarsedemux 297 demuxes the approximately M/N (3) optical signals intoindividual optical signals and transmits the individual signals totransponders 260 g-i via terminal output fiber connections 293 a-c.Transponders 260 g-i are the same type of transponders 260 d-f as shownin FIG. 5.

Transponders 260 g-i convert the LH format optical signals on outputfiber connections 293 a-c into signals suitable for use by CPEs 290pp-rr. Transponders 260 g-i are connected to CPEs 290 pp-rr viaintra-office fibers 251 cc-1, 251 cc-2 and 251 cc-3.

Terminal 225 can also serve as the interface device for the localtraffic (optical signals) intended for CPE 290 pp-rr. Intra-officefibers 251 cc-1, 251 cc-2 and 251 cc-3 are usually physically co-locatedwith terminal 225, but they may incorporate long reach capabilityincluding optical amplifiers to connect to an individual port on aremote CPE 290 via intra-office fiber 251.

The full duplex optical signals also flow in the Z-A direction from CPE290 pp-rr through intra-office fibers 251 dd-1, 251 dd-2 and 251 dd-3 totransponders 260 g-i. Transponders 260 g-i convert the optical signalformats from that used by CPEs 290 pp-rr to a LH format. The convertedLH format signals are sent to terminal coarse mux 297 via terminaloutput fiber connections 293 d-f Coarse mux 298 combines the opticalsignals into an optical mux group for propagation along fiberinterconnection 271 q to metro fiber 252 and on to primary terminal 210.

In both terminal 220 and terminal 225, coarse demux 287, terminal coarsedemux 297, coarse mux 288, and coarse mux 298 may perform the functionof attenuating the individual optical signals. In this way, theinvention can launch or detect the appropriate optical powers withoutthe need of gain equalization provided by optical amplifiers.Furthermore, the attenuation function in extension terminal coarse demux287 and extension terminal coarse mux 288 alleviate the need for tightlycontrolled gain equalization in the extension terminal receiving opticalamplifier 285 and transmitting optical amplifier 286 thereby loweringthe cost.

FIGS. 7 through 10 depict various embodiments of mux and demuxarchitectures which constitute a part of the invention. In FIG. 7, mux500 is made up of two submultiplexers 550 a and 550 b. Submuxers 550 aand 550 b are capable of taking four times N optical signals atdifferent wavelengths and combining them onto one output fiberconnection 515 a and 515 b. N can be any number, for example, 10 asshown in FIG. 7. Mux 500 is capable of taking 8×N (10) optical signalsat different wavelengths and combining them onto one output opticalconnection 505. Thus, the architecture is scaleable up or down in thenumber of wavelengths, for example a 50/25 GHz interleaver may be placedin conjunction with two muxs 500 to form a 16×N multiplexer unit.

The function of an optical interleaver is to combine a “comb” of opticalwavelengths consisting of even and odd numbered wavelengths ordered byintegers as a monotonically increasing sequence with wavelength orfrequency of the optical carrier. The function of an opticalde-interleaver is to separate a “comb” of optical wavelengths consistingof even and odd numbered wavelengths ordered as before. Specificinterleaver or de-interleaver device implementations are known in theart and will not be described further. Interleavers known in the art andcan be obtained from, for example, JDS Uniphase, model numberIBC-LW1D00310.

In what follows, the muxing function will be described along with thedemuxing function that utilizes the same basic architecture andconnectivity. Demuxing is described in parentheses. In the A-Zdirection, Z-A in parentheses, signals enter (leave) mux 500 through aset of 400 GHz filters 540 a-h, known in the art as optical thin filmfilters or layered dielectric optical filters and available from JDSUniphase as model number DWS-2F3883P20.

Filters 540 a and 540 b mux (demux) the received N (10) optical signalstogether (apart) into (from) a “comb” of wavelengths separated by 400GHz and connected to 400/200 GHz interleaver 530 a by fiber connections535 a and 535 b. Because an interleaver for signals in the A-Z directionis also a deinterleaver for signals in the Z-A direction, the terminterleaver will be used to describe both an interleaver anddeinterleaver. Similarly, 400 GHz filter pairs 540 c and 540 d, 540 eand 540 f, and 540 g and 540 h mux (demux) together (apart) the receivedoptical signals into (from) a “comb” of wavelengths separated by 400GHz. The filter pairs 540 c and 540 d, 540 e and 540 f, and 540 g and540 h are in communication with 400/200 GHz interleavers 530 b, 530 cand 530 d, respectively, via 400/200 GHz fiber connections 535 c-h,respectively. 400/200 GHz interleavers 530 a-d combine (separate)optical signals from (for) filters 540 a-h into (from) a single “comb”of wavelengths separated by 200 GHz. The combined (separated) output(input) is transmitted (received) to (from) 200/100 GHz interleaver 520a via 200/100 GHz fiber connection 525 a and 525 b where they arecombined (separated) into (from) a single “comb” of wavelengths 100 GHzapart. Similarly, output from 530 c and 530 d propagate via fiberconnection 525 c and 525 d to (from) interleaver 520 b where they arecombined (separated) into (from) a single “comb” of wavelengths 100 GHzapart Finally, the output (input) “combs” of interleavers 520 a and 520b are transmitted to (from) 100/50 GHz interleaver 510 via 100/50 fiberconnections 515 a and 515 b. 100/50 interleaver 510 combines (separatesout) the single comb of wavelengths to form (from) composite opticalconnection 505 made up of a comb of wavelengths 50 GHz apart.

In reference to FIG. 4, primary terminal 210 is shown to be composed ofa coarse mux 268, a coarse demux 267, a fine mux 266, and a fine demux265. The fine demux 265 and fine mux 266 coincide with the preferredembodiment in FIG. 7 of the combination of 100/50 GHz interleavers 510,200/100 GHz interleavers 520 a-b, and 400/200 GHz interleavers 530 a-d.The coarse demux 267 and coarse mux 268 coincide with the preferredembodiment in FIG. 7 of 400 GHz filters 540 a-h. The coarse mux 288 andcoarse demux 287 in the extension terminals of FIG. 5 and coarse mux 298and coarse demux 297 of FIG. 6 also coincide with 40 Ghz filters 540a-h. Optical connection 505, 100/50 fiber connections 515 a-d, 200/100fiber connections 525 a-c, and fiber connections 535 a-h may function assimple fiber jumpers or optical amplifiers or optical attenuators orsome combination thereof to achieve required fiber distances between thevarious stages of a distributed terminal.

FIG. 8 indicates an alternate embodiment of a mux and demux structure.Mux/demux 600 comprises two submuxs 650 a and demuxs 650 b. Becausemux/demux 600 comprises two submux 650 a and demux 650 b pairs,mux/demux 600 is capable of taking 8×N optical signals (10 are shown inFIG. 8) at different wavelengths and combining them onto oneoutput/input connection 605. Because submux 650 a and demux 650 b arecapable of taking four times N optical signals at different wavelengthsand combining them onto one 2000 GHz fiber connection 615 a and 615 b,the architecture is scaleable up or down in the number of wavelengths.For example, a 4000 GHz Band combiner may be placed in conjunction withtwo mux/demuxes to form a 16×N (10) multiplexer unit.

The function of an optical band splitter/combiner is to split/combine aspecified band of optical wavelengths consisting of tightly spacedoptical wavelengths of typical separation 50 GHz or 25 GHz into or outof two coarse bands of such wavelengths. Specific band splitters or bandcombiner device implementation are well known in the art and notdescribed further. Band filtering devices can be obtained from, forexample, Oplink Corporation model number CR000001111.

In the A-Z direction, signals enter mux/demux 600 through a set of fine50 GHz filters 640 a-h, known in the art. 50 GHz filters 640 a-h mayalso be 25 GHz filters also known in the art. Two examples of fine 50GHz filters 640 are the arrayed waveguide filters and layered dielectricoptical filters available as, for example, JDS Uniphase model numbersAWG-5NBUC003T and DWM-5F8DSX2, respectively.

Starting with fine 50 Hz filter 640 a and 640 b, the N(10) opticalsignals are muxed together into a band of wavelengths contained withinabout 500 GHz and transmitted to 500 GHz band combiner 630 a via 500 GHzfiber connections 635 a and 635 b. Similarly, fine 56 Hz filter pairs640 c and 640 d, 640 e and 640 f and 640 g and 640 h mux N(10) opticalsignals together and transmit the muxed signals to 500 GHz bandcombiners 630 b, 630 c and 630 d respectively via 500 GHz fiberconnections 635 c-h respectively. 500 GHz band combiner 630 a combinesthe optical signals from filters 640 a and 640 b into a single broaderband of wavelengths contained within about 1000 GHz. Similarly, 500 GHzband combiners 630 b-d combine received optical signals into a singlebroader band of wavelengths.

The single broader band of wavelengths from extension band combiners 630a and 630 b are transmitted to 1000 GHz band combiner 620 a via 1000 GHzfiber connections 625 a and 625 b. 1000 GHz band combiner 620 a combinesthe signals from 500 GHz band combiners 630 a and 630 b into a singleband of wavelengths contained within about 2000 GHz. Similarly, 1000 GHzband combiner 620 b combines the wavelengths transmitted from 500 GHzband combiners 630 c and 630 d via 1000 GHz fiber connection. 625 c and625 d into a single band of wavelengths. Each 1000 GHz band combiner 620a and 620 b transmits the single band of wavelengths to 2000 GHzcombiner 610 via 2000 GHz fiber connections 615 a and 615 b. 2000 GHzcombiner 610 combines the received single band of wavelengths into acomposite signal band contained within about 4000 GHz. The compositesignal band is transmitted on output/input connection 605.

In the Z-A direction, 2000 GHz combiner 610 receives a composite signalband contained within about 4000 GHz on output/input connection 605.Because a combiner for signals in the A-Z direction can also be asplitter for signals in the Z-A direction, the term combiner will beused to describe both a combiner and a splitter. 2000 GHz combiner 610splits the composite signal into two single band of wavelengthscontained within about 2000 GHz. The bands of wavelengths within 2000GHz are transmitted to 1000 GHz band combiners 620 a and 620 b via 2000GHz fiber connections 615 a and 615 b. 1000 GHz combiners 620 a and 620b each separate the single band of wavelengths within 2000 GHz into twosingle band of wavelengths within about 1000 GHz. The single band ofwavelengths within 1000 GHz is transmitted from 1000 GHz combiners 620 aand 620 b to 500 GHz band combiners 630 a-d via 1000 GHz fiberconnections 625 a-d. 500 GHz band combiners 630 a-d each split thesingle band of wavelengths contained within about 1000 GHz into a singleband of wavelengths contained within about 500 GHz. The single band ofwavelengths contained within 500 GHz is transmitted from 500 GHz bandcombiners 630 a-d to fine 50 Hz filters 640 a-h via 500 GHz fiberconnections 635 a-h. Fine 50 Hz filters 640 a-d demux the single band ofwavelengths within 500 GHz into N(10) bands of wavelengths wherein theN(10) wavelengths are transmitted out of mux/demux 600.

The fine filter function performed by 50 Hz filters 640 a-h and thecoarse filtering functions performed by the combination of 2000 Ghzcombiner 610, 1000 GHz combiners 620 a and 620 b, and 500 GHz bandcombiners 630 a-d can be separated. The coarse and fine filteringfunctions are reversed in the hierarchy of the interleaver based mux500. Also, output/input connection 605, 2000 GHz fiber connection 615 aand 615 b, 1000 GHz fiber connection 625 a-h, and 500 GHz fiberconnection 635 a-h may function as simple fiber jumpers, opticalamplifiers, optical attenuators, or some combination thereof to achieverequired fiber distances between the various stages of primary terminal210.

A second alternative embodiment of the multiplexing and demultiplexingfunction of the present invention is indicated in FIGS. 9 and 10. Theembodiment depicts a means of implementing a wavelength tunable systemwith primary terminals. Beginning with FIG. 9 tunable demux 700 iscomposed primarily of first optical splitter 710, second opticalsplitter 720 a and 720 b, and third optical splitter 730 a-h Thirdoptical splitter 730 a-h is operationally connected to tunable filters740 via tunable filter fiber connection 731.

In the Z-A direction, first optical splitter 710 receives a compositesignal band contained within about 4000 GHz on tunable input connection705. The embodiment shown is one way of constructing a “tree” whereby asingle band of wavelengths transmitted on tunable input connection 705is demuxed so as separate out groups of wavelengths. The exact natureand combining ratio is not essential. First optical splitter 710 splitsthe composite signal on tunable input connection 705 into two singlebands of wavelengths contained within about 2000 GHz. The bands ofwavelengths within 2000 GHz are transmitted to second optical splitters720 a and 720 b via first splitter fiber connections 715 a and 715 b.Second optical splitters 720 a and 720 b each separate the single bandsof wavelengths within 2000 GHz into two single band of wavelengthswithin about 1000 GHz. The single bands of wavelengths within 1000 GHzare transmitted from second optical splitters 720 a and 720 b to thirdoptical splitters 730 a-h via second splitter fiber connection 725 a-h.Third optical splitters 730 a-h each split the single band ofwavelengths contained within about 1000 GHz into a single band ofwavelengths contained within about 500 GHz. The single band ofwavelengths contained within 500 GHz is transmitted from third opticalsplitters 730 a-h to tunable filters 740 a-x via tunable filter fiberconnections 731.

While the order could be greater, in the preferred embodiment, tunablefilters 740 a-x operate as narrow spectral width bandpass filters with apassband in the order of two and one-half to three times the bandwidthof the carrier frequency; for example, 30 GHz or more for a 10 GHzoptical signal. Tunable filters 740 a-x are tuned to pass any one of thesignals appearing at the outputs of third optical splitters 730 a-h.Optical splitters are known in the art, an example being JDS Uniphasemodel number NEM-221003119. Tunable optical filters are also known inthe art, examples being JDS Uniphase model number VCF050 or NORTEL modelnumber MT-15-025. Tunable input connection 705, first splitter fiberconnections 715 a and 715 b, and second splitter fiber connection 725a-h may function as simple fiber jumpers or optical amplifiers oroptical attenuators or some combination thereof to achieve requiredfiber distances between the various stages of a distributed terminal.

With reference to FIG. 10 tunable mux 701 is composed of first opticalcombiner 711, second optical combiner 760 a and 760 b, and third opticalcombiner 770 a-h. Third optical combiner 770 a-h is operationallyconnected to tunable lasers 780 a-x. Tunable lasers 780 a-x may benarrowly tunable around 200 GHz or broadly tunable, for example, overthe entire C or L band of Erbium-doped fiber amplifiers, the spectralwidth being of the order of 4000 GHz. The laser components may have anoptical output power on the order of 20 mW, wavelength stability on theorder of 2.5 GHz or better, side-mode suppression ratio on the order of35 dB, and relative intensity noise (RIN) on the order of −140 dB.Optical combiners are known in the art, an example being JDS Uniphasemodel number NEM-221003119. Tunable lasers are known in the art, oneexample, JDS Uniphase CQF310/208-19365.

In the Z-A direction, tunable lasers 780 a-x receives a compositesignal. The exact nature and combing ratio is not essential, theembodiment shown is one way of constructing a “tree” whereby one or moreoptical signals generated by one or more different tunable lasers arewavelength muxed so as to appear at output fiber connection 706 as asingle band of wavelengths.

Tunable lasers 780 receive a band of wavelengths. The wavelengths aretuned and transmitted to third optical combiner 770 a-h via tunablelaser fiber connection 775. Third optical combiner 770 a-h muxes thereceived signal from tunable lasers 780 a-x into a single band ofwavelengths within 500 GHz. The single band of wavelengths within 500GHz is transmitted to extension optical combiner 760 a and 760 b viasecond optical fiber connections 726 a-h. Second optical combiners 760 aand 760 b mux the received single band of wavelengths within 500 GHzinto a single band of wavelengths contained within about 1000 GHz. Thesingle band of wavelengths contained within about 1000 GHz istransmitted to first optical combiner 711 via first fiber connections716 a and 716 b. Primary optical combiner 711 muxes the received singleband of wavelengths within 1000 GHz into a single band of wavelengthswithin about 2000 GHz. The single band of wavelengths within about 2000GHz is transmitted over output fiber connection 706.

Output fiber connections 706, first fiber connections 716 a and 716 b,second fiber connections 726 a-h, and tunable laser fiber connection 775may function as simple fiber jumpers or optical amplifiers or opticalattenuators or some combination thereof to achieve required fiberdistances between the various stages of a distributed terminal.

Valid and useful multiplexer and demultiplexer designs can beconstructed with combinations of parts shown in FIGS. 7-10. Finemux/demux 640 a-b from FIG. 8 can individually replace blocks 740 a-x asshown in FIG. 9 or blocks 780 a-x as shown in FIG. 10 to formsplitter/combiner based fixed filters. This alternate arrangement isadvantageous because the cost of components would scale with thedeployed bandwidth. Likewise, tunable components 740 a-x from FIG. 9 and780 a-x from FIG. 10 can individually replace the fixed filters 640 a-hin FIG. 8 to form banded DWDM based tunable filters. Anotheradvantageous embodiment is that of replacing coarse mux/demux filters540 a-h in FIG. 7 with the tunable filter components 780 a-x from FIG. 9and 740 a-x from FIG. 10 to form a mux and demux, respectively.

FIGS. 11 and 12 show different shelf connection configurations of thepreferred embodiment that result from integrating the sub-systems ofFIGS. 4-7 into a distributed terminal system. Each numbered block inFIGS. 11 and 12 is a self-contained shelf within the opticaltransmission system: the master terminal shelf 910 embodies the primaryterminal 210, the slave shelves 920 a-b embody the type one extensionterminal 220; and the dual slaves shelf 925 a-b embody two type twoextension terminals 225 in one unit. In the preferred embodiment, eightoptical mux groups are made up of 10 optical signal-carryingwavelengths.

FIG. 11 depicts a star configuration 900, whereby the submuxs are bothcontained within the master terminal shelf 910 along with one local 400GHz filter. The shelves 910 and 920 a-c are interconnected using fiberjumpers 916, 914 and 912. Dual slave shelves 925 a-b are interconnectedusing fiber jumpers 902, 904, 906 and 908.

FIG. 12 a depicts a second configuration 940 whereby two master shelves911 a and 911 b are utilized to distribute the optical mux groups. Shelf911 a, is similar in function to primary terminal 210, and a 100/506 Hzinterleaver, submux, and a 400 GHz filter. Shelf 911 b, which is alsosimilar in function to primary terminal 210, contains submuxs and a 400GHz filter. The interconnection between master shelves 911 a and 911 bis accomplished by fiber interconnection 932 which is a 100/50 fiberconnection. The configurations 940 and 960 service 8 optical mux groupsor up to 80 optical signal wavelengths in six shelves. Line 941 is anoptical input/output connection. Slave shelves 920 a and 920 b and dualslave shelves 925 a and 925 b contain the same equipment as described inrelation to FIG. 11. Dual slave shelves 925 a and 925 b are coupled tomaster shelf via dual slave-to-master connections 918, 922 and 924.Slave shelves 920 a and 920 b are coupled to master shelf 911 b viaslave-to-master connections 926 and 928. Dual slave-to-masterconnections 918 and 922 may be as long as about 5 km in the preferredembodiment. Slave-to-master connections 926 and 928 may be as long asabout 100 km without additional optical amplifiers.

FIG. 12 b depicts a third configuration 960 similar to configuration 940but utilizing only dual slave shelves 925 a-c attached to the mastershelves 911 a and 911 b. Configuration 960 achieves the highest systemdensity of the configurations of the preferred embodiment. Two mastershelves, 911 a and 911 b, and three dual slave shelves 925 a-c can beused to service all 8 optical mux groups or up to 80 optical signalwavelengths in less than two standard 19 or 23 inch wide seven footequipment racks. Master shelf 911 a is connected to master shelf 911 bby connection 933. Master shelf a and b contain the same components asdescribed in relation to FIG. 12 a. Master shelf a is connected to dualslave shelf 925 a by jumpers 923 and 925. Master shelf 911 a isconnected to dual slave shelf 925 c by jumper 919. Master shelf 911 b isconnected to dual slave shelf 925 b by jumpers 929 and 931. Master shelf911 b is connected to dual slave shelf 925 c through jumper 927.

Dual slave shelves 925 a, b and c contain the same equipment asdescribed in FIG. 12 a. The fiber shelf interconnections 919, 923, 927,925, 929 and 931 may be as long as about 5 km in the preferredembodiment while the master-to-master fiber connection 933 may be on theorder of 100 km (without additional optical amplifiers).

Although the invention has been described with reference to one or morepreferred embodiments, this description is not to be construed in alimiting sense. There is modification of the disclosed embodiments, aswell as alternative embodiments of this invention, which will beapparent to persons of ordinary skill in the art, and the inventionshall be viewed as limited only by reference to the following claims.

1. A primary terminal of an optical transport system, the primaryterminal comprising: a transponder coupled to a customer premiseequipment, wherein the transponder is configured to convert a firstoptical signal from the customer premise equipment into a firstindividual long-haul optical signal, and wherein the first opticalsignal is in a format suitable for use by the customer premiseequipment; a coarse multiplexer coupled to the transponder, wherein thecoarse multiplexer is configured to multiplex the first individuallong-haul optical signal into a first mux group of long-haul opticalsignals; and a fine multiplexer coupled to the coarse multiplexer and toan extension terminal via a metro fiber, wherein the fine multiplexer isconfigured to receive a second mux group of long-haul optical signalsfrom the extension terminal, wherein the fine multiplexer is configuredto multiplex the first mux group from the coarse multiplexer and thesecond mux group from the extension terminal into a third mux group oflong-haul optical signals, and wherein the primary terminal isconfigured to transmit the third mux group over a long-haul network. 2.The primary terminal of claim 1 further comprising an amplifier coupledto the fine multiplexer, wherein the amplifier is configured to amplifythe third mux group from the fine multiplexer.
 3. The primary terminalof claim 1, wherein the coarse multiplexer and the fine multiplexer eachinclude one of an optical interleaver, a banded dense wavelengthdivision multiplexing (DWDM) filter, or a tunable filter.
 4. The primaryterminal of claim 1 further comprising a first demultiplexer coupled tothe long-haul network, wherein the first demultiplexer is configured todemultiplex a fourth mux group of long-haul optical signals from thelong-haul network into a fifth mux group of long-haul optical signalsand a sixth mux group of long-haul optical signals, and wherein theprimary terminal is configured to transmit the fifth mux group to theextension terminal via the metro fiber.
 5. The primary terminal of claim4 further comprising an amplifier coupled to the first demultiplexer,wherein the amplifier is configured to amplify the fourth mux group fromthe long-haul network.
 6. The primary terminal of claim 4 furthercomprising a second demultiplexer coupled to the first demultiplexer andto the transponder, wherein the second demultiplexer is configured todemultiplex the sixth mux group from the first demultiplexer into asecond individual long-haul optical signal.
 7. The primary terminal ofclaim 6, wherein the first demultiplexer comprises a fine demultiplexerand the second demultiplexer comprises a coarse demultiplexer.
 8. Theprimary terminal of claim 6, wherein the first and second demultiplexerseach include one of an optical de-interleaver, a banded dense wavelengthdivision multiplexing (DWDM) filter, or a tunable filter.
 9. The primaryterminal of claim 6, wherein the transponder is further configured toconvert the second individual long-haul optical signal from the seconddemultiplexer into a second optical signal, and wherein the secondoptical signal is in the format suitable for use by the customer premiseequipment.
 10. The primary terminal of claim 9, wherein the primaryterminal is further configured to transmit the second optical signal tothe customer premise equipment.
 11. A method for transporting opticalsignals at a primary terminal, the method comprising: converting a firstoptical signal from a customer premise equipment into a first individuallong-haul optical signal, wherein the first optical signal is in aformat suitable for use by the customer premise equipment; multiplexing,via a coarse multiplexer, the first individual long-haul optical signalinto a first mux group of long-haul optical signals, receiving a secondmux group of long-haul optical signals from an extension terminal via ametro fiber; multiplexing, via a fine multiplexer, the first mux groupand the second mux group into a third mux group of long-haul opticalsignals; and transmitting the third mux group over a long-haul network.12. The method of claim 11 further comprising amplifying the third muxgroup.
 13. The method of claim 11 further comprising: demultiplexing afourth mux group of long-haul optical signals from the long-haul networkinto a fifth mux group of long-haul optical signals and a sixth muxgroup of long-haul optical signals; and transmitting the fifth mux groupto the extension terminal via the metro fiber.
 14. The method of claim13 further comprising amplifying the fourth mux group.
 15. The method ofclaim 13 demultiplexing the sixth mux group into a second individuallong-haul optical signal.
 16. The method of claim 15 further comprisingconverting the second individual long-haul optical signal into a secondoptical signal, wherein the second optical signal is in the formatsuitable for use by the customer premise equipment.
 17. The method ofclaim 16 further comprising transmitting the second optical signal tothe customer premise equipment.
 18. An optical transport system fortransporting optical signals, the optical transport system comprising:an extension terminal coupled to a first customer premise equipment; anda primary terminal coupled to the extension terminal via a metro fiber,wherein the primary terminal comprises a coarse multiplexer and a finemultiplexer, wherein the extension terminal is configured to receive afirst optical signal suitable for use by the first customer premiseequipment and to convert the first optical signal into a firstindividual long-haul optical signal, wherein the extension terminal isfurther configured to multiplex the first individual long-haul opticalsignal into a first mux group of long-haul optical signals and totransmit the first mux group to the fine multiplexer of the primaryterminal via the metro fiber.
 19. The optical transport system of claim18, wherein the primary terminal is configured to transmit the first muxgroup over a long-haul network.
 20. The optical transport system ofclaim 18, wherein the primary terminal is coupled to a second customerpremise equipment, wherein is the primary terminal configured to receivea second optical signal suitable for use by the second customer premiseequipment and to convert the second optical signal into a secondindividual long-haul optical signal, and wherein the primary terminal isfurther configured to multiplex, via the coarse multiplexer, the secondindividual long-haul optical signal into a second mux group of long-hauloptical signals.
 21. The optical transport system of claim 20, whereinthe primary terminal is further configured to multiplex, via the finemultiplexer, the first mux group and the second mux group into a thirdmux group of long-haul optical signals, and wherein the primary terminalis further configured to transmit the third mux group over a long-haulnetwork.
 22. The optical transport system of claim 21, wherein theprimary terminal is further configured to amplify the third mux group.23. The optical transport system of claim 18, wherein the extensionterminal is further configured to amplify the first mux group.
 24. Anoptical transport system for transporting optical signals, the opticaltransport system comprising: an extension terminal coupled to a firstcustomer premise equipment; and a primary terminal coupled to theextension terminal via a metro fiber, wherein the primary terminalcomprises a coarse demultiplexer and a fine demultiplexer, wherein theprimary terminal is configured to receive a first mux group of long-hauloptical signals from a long-haul network, wherein the fine demultiplexerconfigured to demultiplex the first mux group into a second mux group oflong-haul optical signals and a third mux group of long-haul opticalsignals, wherein the coarse demultiplexer is configured to demultiplexthe second mux group, wherein the primary terminal is further configuredto transmit the third mux group to the extension terminal via the metrofiber, wherein the extension terminal is configured to demultiplex thethird mux group into a first individual long-haul signal, and whereinthe extension terminal is further configured to convert the firstindividual long-haul signal into a first optical signal suitable for useby the first customer premise equipment and to transmit the firstoptical signal to the first customer premise equipment.
 25. The opticaltransport system of claim 24, wherein the primary terminal is coupled toa second customer premise equipment, wherein the coarse demultiplexer isconfigured to demultiplex the second mux group into a second individuallong-haul optical signal, and wherein the primary terminal is furtherconfigured to convert the second individual long-haul optical signalinto a second optical signal suitable for use by the second customerpremise equipment and to transmit the second optical signal to thesecond customer premise equipment.
 26. The optical transport system ofclaim 24, wherein the primary terminal is further configured to amplifythe first mux group.
 27. The optical transport system of claim 24,wherein the extension terminal is further configured to amplify thesecond mux group.
 28. A primary terminal of an optical transport system,the primary terminal comprising: a fine demultiplexer coupled to along-haul network and to an extension terminal, wherein the finedemultiplexer is configured to demultiplex a first mux group oflong-haul optical signals from the long-haul network into a second muxgroup of long-haul optical signals and a third mux group of long-hauloptical signals; a coarse demultiplexer coupled to the finedemultiplexer, wherein the coarse demultiplexer is configured todemultiplex the second mux group into a first individual long-hauloptical signal; and a transponder coupled to the coarse demultiplexerand to a customer premise equipment, wherein the transponder isconfigured to convert the first individual long-haul optical signal intoa first optical signal that is in a format suitable for use by thecustomer premise equipment, wherein the transponder is configured totransmit the first optical signal to the customer premise equipment, andwherein the primary terminal is configured to transmit the third muxgroup to the extension terminal over a metro fiber.
 29. The primaryterminal of claim 28 further comprising an amplifier coupled between thelong-haul network and the fine demultiplexer, wherein the amplifier isconfigured to amplify the first mux group from the long-haul network.30. The primary terminal of claim 28, wherein the coarse demultiplexerand the fine demultiplexer each include one of an optical interleaver, abanded dense wavelength division multiplexing (DWDM) filter, or atunable filter.
 31. The primary terminal of claim 28, wherein thetransponder is further configured to receive a second optical signalfrom a second customer premise equipment and to convert the secondoptical signal into a second individual long-haul optical signal. 32.The primary terminal of claim 31 further comprising a coarse multiplexercoupled to the transponder, wherein the coarse multiplexer is configuredto multiplex the second individual long-haul optical signal into afourth mux group of long-haul optical signals.
 33. The primary terminalof claim 32 further comprising a fine multiplexer coupled to the coarsemultiplexer and the extension terminal, wherein the fine multiplexer isconfigured to receive a fifth mux group of long-haul optical signalsfrom the extension terminal.
 34. The primary terminal of claim 33,wherein the fine multiplexer is configured to multiplex the fourth muxgroup and the fifth mux group into a sixth mux group of long-hauloptical signals.
 35. The primary terminal of claim 34 further comprisingan amplifier coupled to the fine multiplexer, wherein the amplifier isconfigured to amplify the sixth mux group from the fine multiplexer. 36.The primary terminal of claim 34, wherein the primary terminal isconfigured to transmit the sixth mux group over the long-haul network.